This invention is related to apparatus for perforating oil wells, and is more particularly related to a detonator assembly for initiating oil well perforator units in a perforating gun assembly.
As is known in the art, perforating gun assemblies are used in the production of oil and gas when it is desired to provide perforations through an oil well casing and into a hydrocarbon producing formation to provide access from the formation into the well bore such that oil and gas may be produced.
After the oil well has been drilled, a steel casing is lowered into the well bore and cemented into place to protect the well bore and to prevent migration of formation fluid from one formation to another.
A perforating gun is then lowered into the steel casing and perforations are made at a desired spacing through the steel liner and into the formation such that hydrocarbons in the desired formation may flow into the oil well bore and from there be produced to the surface.
In the past, perforating gun assemblies have been transported to the oil well site in a disassembled or partially disassembled condition. For safety reasons, the shaped charge perforating units have been transported separate from the detonating devices such that if the detonating devices were accidentally discharged, the shaped charge perforating units would not be detonated in turn.
Attempts have been made to provide a detonating assembly which may be installed in a gun assembly such that the gun assembly can be transported in the fully assembled condition. Such an apparatus is disclosed in U.S. Pat. No. 4,011,815 issued to Jose Garcia Mar. 15, 1977. The apparatus disclosed in the aforementioned patent is not entirely satisfactory in that a passageway is provided which is difficult to adequately seal to prevent well fluids from entering the gun assembly through the detonating apparatus.
In the apparatus disclosed herein, two housing members are provided which are arranged to allow rotatable movement therebetween from a safe position to an armed position. This rotatable movement is provided by applying torque to a bull plug sealed in one end of the tubular charge carrier of the gun assembly.
The detonator of the gun assembly is enclosed in an explosive absorptive cavity, and is further arranged to be aligned with a booster in the detonating train of the well perforator units when the apparatus is in the armed position, and is further arranged to be isolated from the booster when the apparatus is in the safe position. A safety pin means is further provided which further protects the mentioned booster when the apparatus is in the safe position.
If the detonator should be accidentally exploded when the apparatus is in the safe position, the explosion will be absorbed by the housing members and the booster will be covered by the safety pin such that the detonator blast will not be propagated to the booster and the well perforator units will thus not be exploded accidentally.
It can be seen that a well perforating gun assembly is provided which may be transported to the well site in a fully assembled condition and with the detonator assembly in the safe position. After arrival at the well site, the gun assembly may be fully armed by simply rotating a plug at one end of the gun assembly to move the enclosed detonator into alignment with a booster.
Appropriate sealing means is provided between the end plug and the gun assembly such that the end plug may be freely rotated without disturbing the seal between the plug and the gun assembly. Thus, the disclosed gun assembly is protected from invasion of well bore fluids, and the well perforating units and detonator within the gun assembly are desensitized from well bore fluid pressure.
Visual means are also provided to give a visual indication as to whether the gun assembly is in the safe or the armed condition.